One electrophotographic image forming device is known as a printer that includes a device body; a drum unit having a photosensitive drum and a charger and removably mounted in the device body; a developing cartridge mounted in the drum unit and having a developing roller; and an exposure device for exposing the photosensitive drum.
In this type of the printer, the charger first applies charge to the surface of the photosensitive drum, after which the exposure device selectively removes charge from the surface of the photosensitive drum to form an electrostatic latent image thereon. The developing roller supplies toner to the electrostatic latent image on the photosensitive drum to form a toner image thereon. The toner image is then transferred from the surface of the photosensitive drum onto paper to form an image on the paper.